This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The problem of a strong manganese signal is very well known in high-field EPR. Unfortunately, because of the peculiarities of its spin-lattice relaxation this signal is nearly ubiquitous in biological samples even with careful sample preparation techniques. Since biological samples usually need quite high modulation amplitude to enhance the signal to noise ratio, the narrow impurity lineshape is often overmodulated and it is not easy to subtract the impurity line. We have started work on a computational algorithm to allow for accurate subtraction of the impurity line in order to recover the desired spectrum for subsequent analysis.